This document relates to the use of a modified ground tire rubber based asphalt additive and a new asphalt and asphalt concrete compositions incorporating that additive. The modified ground tire rubber based additive described herein is made by mixing ground tire rubber with a second component selected from a group consisting of a gelling clay, a reactive agent, an elastomer, a plastomer, a handling and agglomerating agent and mixtures thereof as well as a compatibilizer. During the mixing and agglomerating process, the ground tire rubber undergoes frictional heating, shear, centering, coalescence and fusion to promote molecular entanglements and polar-polar interactions between the ground tire rubber particles and other components of the additive including any elastomer and plastomer. These molecular entanglements and polar-polar interactions are further enhanced by the compatibilizer provided in the additive. The ground tire rubber particles in the resulting modified ground tire rubber based additive have undergone a physical change that renders them better suited for use as an asphalt additive.
More particularly, the modified ground tire rubber based additive is in the form of granules, of perhaps 0.3-3.0 mm in diameter that are easy to handle. Further, the modified ground tire rubber based additive enhances both the high temperature and low temperature performance of the asphalt to which it is added. More specifically, the elastomeric properties of the ground tire rubber serve to impart a flexibility to the asphalt at low temperatures so that it is better able to resist cracking in response to freeze-thaw cycles. However, when used alone, the elastomer of the ground tire rubber does nothing to improve but, in fact, degrades the high temperature performance of the asphalt by reducing its resistance to longitudinal rutting and high-temperature induced micro-cracking of the road surface. In contrast, the modified ground tire rubber additive disclosed herein includes ground tire rubber that has been modified and subjected to molecular entanglements and polar-polar interactions with plastomers that serve to increase the stiffness of the asphalt to improve the high temperature performance of the asphalt so that it will better resist longitudinal rutting and microcracking when subjected to high temperatures. Advantageously, the additive provides the proper balance between plastomer properties and elastomer properties to actually enhance both high temperature and low temperature performance of any asphalt incorporating the additive. Further, this is done in a single additive with the proper proportions to provide the best results. Such a single additive is simple and convenient to use. Further, such a single additive eliminates any potential for human error of adding too much plastomer or too much elastomer when performing onsite asphalt mixing.
Thus, it should be appreciated that this document not only describes a novel modified ground tire rubber based asphalt additive particularly suited for use in asphalt roadways but also a new range of asphalt and asphalt concrete compositions, made possible with the use of additives at the agglomeration stage that offer vastly superior features and benefits in asphalt when compared to unprocessed ground tire rubber.